LED lights, at least 2 (can be found in hardware stores)
4 AA batteries (1.5V each)
Battery holder for 4 batteries with wires (can be found in hardware stores)
Optional: motor and buzzer

Make the playdoughs:

Mix all the ingredients in a large bowl.
Knead and add flour or water if needed.
Note: the insulating dough is gooey and much less pleasant than the conducting dough.

Test different kind of circuits:

Insert the batteries into the battery holder

Circuit A

Make 2 small balls from the conductive playdough.
Connect each ball to one wire of the battery holder.
Stick the LED in the playdough, one leg in each ball. Make sure the balls do not touch each other.
Did the LED lit? If not, try to reverse its legs in the playdough.
Now make a contact between the balls. What happened to the light?

Circuit B

Exchange the conductive playdough with the insulating one.
Did the LED lit? What about if you reverse its legs in the playdough?

Circuit C

Make 2 small balls of conductive playdough and 1 from the insulating dough.
Set the insulating ball in the middle between the conductive ones.
Connect one wire to each ball and stick the LED legs in the conductive balls.
Did the LED lit? If not, try to reverse its legs in the playdough.

Circuit D – Get Creative

Try to sep up your circuits with different shapes and configurations of both playdoughs.
Change the LED with other electrical component you have.

What’s going on here?

How an electrical circuit works?

Electricity is the flow of electrons in a loop made of conductive materials, materials that allow that flow. In order for a circuit to work we need a power source (the batteries in our case). In an electric circuit, the electrons always flow form the negative terminal of the power source to the positive terminal, and from the positive terminal to the negative one when flowing inside the power source. Since we can’t see the electrons , in order to know the circuit works, we need an electrical component that will tell us electricity flows, like LED, buzzer, computer, washing machine and so many more!

How come the playdough can be conductive or insulating?

Look again at the ingredients list. See the differences? In the conductive dough we used salt and cream of tartar. In the insulating one we replaced the salt with sugar, the tap water with distilled water and didn’t add cream of tartar at all.
Why? Because the conductive properties of all these ingredients!
Table salt is a chemical that is made of ions, sodium ions and chloride ions. That means it contains electrical charges which allows the flow of electrons. Same goes with the cream of tartar. Cream of tartar is another type of salt, although it doesn’t contain sodium or chloride, but other kind of ions. Cream of tartar, by the way, is the magic ingredient that turns a regular dough into a playdough, and that’s the reason the insulating playdough is not as fun to play with.
In the insulating playdough, we exchanged the salt with sugar. Sugar, doesn’t contain ions, thus it doesn’t conduct electricity. Same with distilled water. Distilled water is water from which the salts were removed, and since it contains no salt, it doesn’t conduct electricity. Did you know, the very low levels of different salts in our tap water are what makes tap water tastier than the taste-less distilled water.

So now that we understand what’s going on in the playdough lets talk about the circuits we built:

Why doesn’t the LED always work?
LED stands for Light Emitting Diode. As opposed to a wire or incandescent light, a diode is en electrical component that conduct electricity only in one direction. Therefore, the direction of the LED in the circuit is crucial for lighting it.

Why the light went off when the 2 conductive balls were brought into contact?

Well, what we did here is called short circuit. It means we gave the electrons a shortcut, an easier way to go through the circuit. And since nature always prefers the easiest route, most of the electrons take that shortcut and the LED doesn’t get enough electrons or electricity to lit.

Connect one wire to the first ball and the other to the last ball in the row.

Stick an LED in the first and middle balls, bridging them. Stick a second LED in the middle and last balls, bridging them. Reverse their directions, if needed.

Now pull out one of the LEDs. What happened to the other LED?

Mix them together: Set a circuit that contains both in parallel and series components

Using the series circuit set before, add another LED, bridging 2 balls.

if needed, reverse the directions of the LED.

What’s going on here?

Electrical circuits can be assembled in 2 basic configurations: in parallel and in series.

As you’ve seen, in a parallel circuit the components (LEDs in our case) share a common junction point. They all see the same voltage (which is a measure for energy) form the power source (the batteries in our case), no matter if we use the same component or not. However, the current (number of electrons flowing through them) depends on the components’ resistance, on how much the components oppose the flow of electron. The resistance depends on the nature on the component.

You can think of it as a multi-lane road. If one lane has pot holes, cars will drive slower in this lane, but that will not affect the speed of traffic in other lanes.

A series circuit works exactly the opposite way. The component are connected one after another in a row like train cars. The current is the same through all the components, but the voltage depends on their resistance.

In the road analogy it would look like a single lane road. When traffic moves from a well maintained section to a bumpy section, it will slow down everyone.

So the circuit looks different, but what’s all the fuss about? Remember when you pulled out one of the LEDs in the series circuit and all the lights went off? That’s because it’s a series circuit! As simple as that. When one component pulled out, the circuit is open and the electrons cannot flow.

But when you pulled out one LED from the parallel circuit it looks like it doesn’t matter, all the other components were still on. It’s true, opening the circuit in that one point doesn’t open the whole circuit and the other LEDs stay on. However, it does matter, the load on the circuit is lower now and the components left in the circuit can work with higher power.

Where do we find these circuits in our daily life?

Practically everywhere!

Some Christmas lights lines are set in series configuration. In this case, just one broken light in the line will turn off the whole line.

As an example of parallel circuit, you can think about your home. The rooms are connected in parallel to each other. Thus, turning on or off the light in one room doesn’t affect the lights in other rooms.

Did you know? Parallel and series configurations are not limited to electricity.

Our body works in parallel and series in many ways. For example, the hair connected to the head in parallel. The fall of one hair strand doesn’t affect the rest of the hair.

Parts of the blood system work in series. The same blood that goes to your toes tips travel through the torso, a leg and a foot before reaching a toe.

Now tell us:

What other applications of parallel and series configuration can you think of?

On November 22, 2012, Pueblo Science and the University of Toronto family care office brought hands-on science activities that parents could do with their children to postdocs, students, faculty and staff of University of Toronto. Prof. Cynthia Goh introduced the history of Pueblo Science and gave a short talk on the importance of having parents engaged in science together with their kids. Alon Eisenstein and Neta Raz instructed the activity. They started with gelation, turning tatziki into gel balls served on top of cucumber slices, the tatziki explodes in your mouth after biting the gel, it was delicious! They then followed it with dessert, using chocolate to calculate the speed of light! Afterwards, the parents made their own playdough, played with it and learned series and parallel circuits in the process!